Angiotensin-converting enzyme (angiotensin I-converting enzyme; also referred to as “ACE” in the present specification) is an enzyme that converts angiotensin I into angiotensin II. Angiotensin II has the action of increasing blood pressure by, for example, contracting blood vessels. It is known that when the action of ACE is inhibited, the production of angiotensin II is suppressed, thereby showing an anti-hypertensive effect. Accordingly, ACE-inhibitory substances are used, for example, as active ingredients of blood pressure-lowering agents, and food-related components suitable for people with elevated blood pressure.
As the number of patients with hypertension and people with elevated blood pressure has recently been increasing, demand has grown for substances that are safe and have excellent ACE inhibitory activity, and research and development of such substances have been actively conducted. One example of such research and development is the search for peptides that have ACE inhibitory activity. For example, PTL 1 reports that 3 tripeptides having blood pressure-lowering action by ACE inhibition were discovered from a thermolysin digestion product of sesame, PTL 2 reports that a peptide having ACE inhibitory activity was discovered from a digestion product of pig-derived protein with pepsin, PTL 3 reports that a peptide having ACE inhibitory activity was discovered from an enzymatic digestion product of fish-derived protein, PTL 4 reports that a peptide having sequences of decomposed fragments of angiotensin II has ACE inhibitory activity, and PTL 5 reports a dipeptide having ACE inhibitory activity.